NAME

erl - The Erlang Emulator

DESCRIPTION

The erl program starts an Erlang runtime system. The exact details (for
example, whether erl is a script or a program and which other programs
it calls) are system-dependent.
Windows users probably wants to use the werl program instead, which
runs in its own window with scrollbars and supports command-line
editing. The erl program on Windows provides no line editing in its
shell, and on Windows 95 there is no way to scroll back to text which
has scrolled off the screen. The erl program must be used, however, in
pipelines or if you want to redirect standard input or output.

EXPORTS

erl<arguments>
Starts an Erlang runtime system.
The arguments can be divided into emulatorflags, flags and
plainarguments:
* Any argument starting with the character + is interpreted as
an emulatorflag. .br .br As indicated by the name, emulator
flags controls the behavior of the emulator. .br .br
* Any argument starting with the character - (hyphen) is
interpreted as a flag which should be passed to the Erlang
part of the runtime system, more specifically to the init
system process, see init(3erl). .br .br The init process
itself interprets some of these flags, the initflags. It
also stores any remaining flags, the userflags. The latter
can be retrieved by calling init:get_argument/1. .br .br It
can be noted that there are a small number of "-" flags
which now actually are emulator flags, see the description
below. .br .br
* Plain arguments are not interpreted in any way. They are
also stored by the init process and can be retrieved by
calling init:get_plain_arguments/0. Plain arguments can
occur before the first flag, or after a -- flag.
Additionally, the flag -extra causes everything that follows
to become plain arguments. .br .br
Example:
% erl +W w -sname arnie +R 9 -s my_init -extra +bertie
(arnie@host)1> init:get_argument(sname).
{ok,[["arnie"]]}
(arnie@host)2> init:get_plain_arguments().
["+bertie"]
Here +Ww and +R9 are emulator flags. -smy_init is an init
flag, interpreted by init. -snamearnie is a user flag, stored
by init. It is read by Kernel and will cause the Erlang runtime
system to become distributed. Finally, everything after -extra
(that is, +bertie) is considered as plain arguments.
% erl -myflag 1
1> init:get_argument(myflag).
{ok,[["1"]]}
2> init:get_plain_arguments().
[]
Here the user flag -myflag1 is passed to and stored by the init
process. It is a user defined flag, presumably used by some user
defined application.

FLAGS

In the following list, init flags are marked (init flag). Unless
otherwise specified, all other flags are user flags, for which the
values can be retrieved by calling init:get_argument/1. Note that the
list of user flags is not exhaustive, there may be additional,
application specific flags which instead are documented in the
corresponding application documentation.
--(init flag)
Everything following -- up to the next flag ( -flag or +flag) is
considered plain arguments and can be retrieved using
init:get_plain_arguments/0.
-ApplicationParVal
Sets the application configuration parameter Par to the value Val
for the application Application, see app(4) and
application(3erl).
-args_fileFileName
Command line arguments are read from the file FileName. The
arguments read from the file replace the ’ -args_fileFileName’
flag on the resulting command line.
The file FileName should be a plain text file and may contain
comments and command line arguments. A comment begins with a #
character and continues until next end of line character.
Backslash (\) is used as quoting character. All command line
arguments accepted by erl are allowed, also the -args_fileFileName flag. Be careful not to cause circular dependencies
between files containing the -args_file flag, though.
The -extra flag is treated specially. Its scope ends at the end
of the file. Arguments following an -extra flag are moved on the
command line into the -extra section, i.e. the end of the command
line following after an -extra flag.
-async_shell_start
The initial Erlang shell does not read user input until the
system boot procedure has been completed (Erlang 5.4 and later).
This flag disables the start synchronization feature and lets the
shell start in parallel with the rest of the system.
-bootFile
Specifies the name of the boot file, File.boot, which is used to
start the system. See init(3erl). Unless File contains an
absolute path, the system searches for File.boot in the current
and $ROOT/bin directories.
Defaults to $ROOT/bin/start.boot.
-boot_varVarDir
If the boot script contains a path variable Var other than $ROOT,
this variable is expanded to Dir. Used when applications are
installed in another directory than $ROOT/lib, see
systools:make_script/1,2.
-code_path_cache
Enables the code path cache of the code server, see code(3erl).
-compileMod1Mod2...
Compiles the specified modules and then terminates (with non-zero
exit code if the compilation of some file did not succeed).
Implies -noinput. Not recommended - use erlc instead.
-configConfig
Specifies the name of a configuration file, Config.config, which
is used to configure applications. See app(4) and
application(3erl).
-connect_allfalse
If this flag is present, global will not maintain a fully
connected network of distributed Erlang nodes, and then global
name registration cannot be used. See global(3erl).
-cookieCookie
Obsolete flag without any effect and common misspelling for
-setcookie. Use -setcookie instead.
-detached
Starts the Erlang runtime system detached from the system
console. Useful for running daemons and backgrounds processes.
-emu_args
Useful for debugging. Prints out the actual arguments sent to the
emulator.
-envVariableValue
Sets the host OS environment variable Variable to the value Value
for the Erlang runtime system. Example:
% erl -env DISPLAY gin:0
In this example, an Erlang runtime system is started with the
DISPLAY environment variable set to gin:0.
-evalExpr(init flag)
Makes init evaluate the expression Expr, see init(3erl).
-extra(init flag)
Everything following -extra is considered plain arguments and can
be retrieved using init:get_plain_arguments/0.
-heart
Starts heart beat monitoring of the Erlang runtime system. See
heart(3erl).
-hidden
Starts the Erlang runtime system as a hidden node, if it is run
as a distributed node. Hidden nodes always establish hidden
connections to all other nodes except for nodes in the same
global group. Hidden connections are not published on neither of
the connected nodes, i.e. neither of the connected nodes are part
of the result from nodes/0 on the other node. See also hidden
global groups, global_group(3erl).
-hostsHosts
Specifies the IP addresses for the hosts on which Erlang boot
servers are running, see erl_boot_server(3erl). This flag is
mandatory if the -loaderinet flag is present.
The IP addresses must be given in the standard form (four decimal
numbers separated by periods, for example "150.236.20.74". Hosts
names are not acceptable, but a broadcast address (preferably
limited to the local network) is.
-idId
Specifies the identity of the Erlang runtime system. If it is run
as a distributed node, Id must be identical to the name supplied
together with the -sname or -name flag.
-init_debug
Makes init write some debug information while interpreting the
boot script.
-instr(emulator flag)
Selects an instrumented Erlang runtime system (virtual machine)
to run, instead of the ordinary one. When running an instrumented
runtime system, some resource usage data can be obtained and
analysed using the module instrument. Functionally, it behaves
exactly like an ordinary Erlang runtime system.
-loaderLoader
Specifies the method used by erl_prim_loader to load Erlang
modules into the system. See erl_prim_loader(3erl). Two Loader
methods are supported, efile and inet. efile means use the local
file system, this is the default. inet means use a boot server on
another machine, and the -id, -hosts and -setcookie flags must be
specified as well. If Loader is something else, the user supplied
Loader port program is started.
-make
Makes the Erlang runtime system invoke make:all() in the current
working directory and then terminate. See make(3erl). Implies
-noinput.
-manModule
Displays the manual page for the Erlang module Module. Only
supported on Unix.
-modeinteractive|embedded
Indicates if the system should load code dynamically (
interactive), or if all code should be loaded during system
initialization ( embedded), see code(3erl). Defaults to
interactive.
-nameName
Makes the Erlang runtime system into a distributed node. This
flag invokes all network servers necessary for a node to become
distributed. See net_kernel(3erl). It is also ensured that epmd
runs on the current host before Erlang is started. See epmd(1).
The name of the node will be Name@Host, where Host is the fully
qualified host name of the current host. For short names, use the
-sname flag instead.
-noinput
Ensures that the Erlang runtime system never tries to read any
input. Implies -noshell.
-noshell
Starts an Erlang runtime system with no shell. This flag makes it
possible to have the Erlang runtime system as a component in a
series of UNIX pipes.
-nostick
Disables the sticky directory facility of the Erlang code server,
see code(3erl).
-oldshell
Invokes the old Erlang shell from Erlang 3.3. The old shell can
still be used.
-paDir1Dir2...
Adds the specified directories to the beginning of the code path,
similar to code:add_pathsa/1. See code(3erl). As an alternative
to -pa, if several directories are to be prepended to the code
and the directories have a common parent directory, that parent
directory could be specified in the ERL_LIBS environment
variable. See code(3erl).
-pzDir1Dir2...
Adds the specified directories to the end of the code path,
similar to code:add_pathsz/1. See code(3erl).
-remshNode
Starts Erlang with a remote shell connected to Node.
-rshProgram
Specifies an alternative to rsh for starting a slave node on a
remote host. See slave(3erl).
-runMod[Func[Arg1,Arg2,...]](init flag)
Makes init call the specified function. Func defaults to start.
If no arguments are provided, the function is assumed to be of
arity 0. Otherwise it is assumed to be of arity 1, taking the
list [Arg1,Arg2,...] as argument. All arguments are passed as
strings. See init(3erl).
-sMod[Func[Arg1,Arg2,...]](init flag)
Makes init call the specified function. Func defaults to start.
If no arguments are provided, the function is assumed to be of
arity 0. Otherwise it is assumed to be of arity 1, taking the
list [Arg1,Arg2,...] as argument. All arguments are passed as
atoms. See init(3erl).
-setcookieCookie
Sets the magic cookie of the node to Cookie, see
erlang:set_cookie/2.
-shutdown_timeTime
Specifies how long time (in milliseconds) the init process is
allowed to spend shutting down the system. If Time ms have
elapsed, all processes still existing are killed. Defaults to
infinity.
-snameName
Makes the Erlang runtime system into a distributed node, similar
to -name, but the host name portion of the node name Name@Host
will be the short name, not fully qualified.
This is sometimes the only way to run distributed Erlang if the
DNS (Domain Name System) is not running. There can be no
communication between nodes running with the -sname flag and
those running with the -name flag, as node names must be unique
in distributed Erlang systems.
-smp[enable|auto|disable]-smpenable and -smp starts the Erlang runtime system with SMP
support enabled. This may fail if no runtime system with SMP
support is available. -smpauto starts the Erlang runtime system
with SMP support enabled if it is available and more than one
logical processor are detected. -smpdisable starts a runtime
system without SMP support. By default -smpauto will be used
unless a conflicting parameter has been passed, then -smpdisable
will be used. Currently only the -hybrid parameter conflicts with
-smpauto.
NOTE: The runtime system with SMP support will not be available
on all supported platforms. See also the +S flag.
-version(emulator flag)
Makes the emulator print out its version number. The same as erl+V.

EMULATORFLAGS

erl invokes the code for the Erlang emulator (virtual machine), which
supports the following flags:
+asize
Suggested stack size, in kilowords, for threads in the async-
thread pool. Valid range is 16-8192 kilowords. The default
suggested stack size is 16 kilowords, i.e, 64 kilobyte on 32-bit
architectures. This small default size has been chosen since the
amount of async-threads might be quite large. The default size is
enough for drivers delivered with Erlang/OTP, but might not be
sufficiently large for other dynamically linked in drivers that
use the driver_async() functionality. Note that the value passed
is only a suggestion, and it might even be ignored on some
platforms.
+Asize
Sets the number of threads in async thread pool, valid range is
0-1024. Default is 0.
+B[c|d|i]
The c option makes Ctrl-C interrupt the current shell instead of
invoking the emulator break handler. The d option (same as
specifying +B without an extra option) disables the break
handler. The i option makes the emulator ignore any break signal.
If the c option is used with oldshell on Unix, Ctrl-C will
restart the shell process rather than interrupt it.
Note that on Windows, this flag is only applicable for werl, not
erl ( oldshell). Note also that Ctrl-Break is used instead of
Ctrl-C on Windows.
+c Disable compensation for sudden changes of system time.
Normally, erlang:now/0 will not immediately reflect sudden
changes in the system time, in order to keep timers (including
receive-after) working. Instead, the time maintained by
erlang:now/0 is slowly adjusted towards the new system time.
(Slowly means in one percent adjustments; if the time is off by
one minute, the time will be adjusted in 100 minutes.)
When the +c option is given, this slow adjustment will not take
place. Instead erlang:now/0 will always reflect the current
system time. Note that timers are based on erlang:now/0. If the
system time jumps, timers then time out at the wrong time.
+d If the emulator detects an internal error (or runs out of
memory), it will by default generate both a crash dump and a core
dump. The core dump will, however, not be very useful since the
content of process heaps is destroyed by the crash dump
generation.
The +d option instructs the emulator to only produce a core dump
and no crash dump if an internal error is detected.
Calling erlang:halt/1 with a string argument will still produce a
crash dump.
+hSize
Sets the default heap size of processes to the size Size.
+Ktrue|false
Enables or disables the kernel poll functionality if the emulator
supports it. Default is false (disabled). If the emulator does
not support kernel poll, and the +K flag is passed to the
emulator, a warning is issued at startup.
+l Enables auto load tracing, displaying info while loading code.
+MFlagValue
Memory allocator specific flags, see erts_alloc(3erl) for further
information.
+PNumber
Sets the maximum number of concurrent processes for this system.
Number must be in the range 16..134217727. Default is 32768.
+RReleaseNumber
Sets the compatibility mode.
The distribution mechanism is not backwards compatible by
default. This flags sets the emulator in compatibility mode with
an earlier Erlang/OTP release ReleaseNumber. The release number
must be in the range 7..<currentrelease>. This limits the
emulator, making it possible for it to communicate with Erlang
nodes (as well as C- and Java nodes) running that earlier
release.
For example, an R10 node is not automatically compatible with an
R9 node, but R10 nodes started with the +R9 flag can co-exist
with R9 nodes in the same distributed Erlang system, they are
R9-compatible.
Note: Make sure all nodes (Erlang-, C-, and Java nodes) of a
distributed Erlang system is of the same Erlang/OTP release, or
from two different Erlang/OTP releases X and Y, where all Y nodes
have compatibility mode X.
For example: A distributed Erlang system can consist of R10
nodes, or of R9 nodes and R9-compatible R10 nodes, but not of R9
nodes, R9-compatible R10 nodes and "regular" R10 nodes, as R9 and
"regular" R10 nodes are not compatible.
+r Force ets memory block to be moved on realloc.
+SSchedulers:SchedulerOnline
Sets the amount of scheduler threads to create and scheduler
threads to set online when SMP support has been enabled. Valid
range for both values are 1-1024. If the Erlang runtime system is
able to determine the amount of logical processors configured and
logical processors available, Schedulers will default to logical
processors configured, and SchedulersOnline will default to
logical processors available; otherwise, the default values will
be 1. Schedulers may be omitted if :SchedulerOnline is not and
vice versa. The amount of schedulers online can be changed at run
time via erlang:system_flag(schedulers_online,SchedulersOnline).
This flag will be ignored if the emulator doesn’t have SMP
support enabled (see the -smp flag).
+sFlagValue
Scheduling specific flags.
+sbtBindType
Set scheduler bind type. Currently valid BindTypes:
u Same as erlang:system_flag(scheduler_bind_type,unbound).
ns Same as erlang:system_flag(scheduler_bind_type,no_spread).
ts Same as erlang:system_flag(scheduler_bind_type,thread_spread).
ps Same as erlang:system_flag(scheduler_bind_type,processor_spread).
s Same as erlang:system_flag(scheduler_bind_type,spread).
nnts
Same as erlang:system_flag(scheduler_bind_type,no_node_thread_spread).
nnps
Same as erlang:system_flag(scheduler_bind_type,no_node_processor_spread).
tnnps
Same as erlang:system_flag(scheduler_bind_type,thread_no_node_processor_spread).
db Same as erlang:system_flag(scheduler_bind_type,default_bind).
Binding of schedulers are currently only supported on newer Linux
and Solaris systems.
If no CPU topology is available when the +sbt flag is processed and
BindType is any other type than u, the runtime system will fail to
start. CPU topology can be defined using the +sct flag. Note that
the +sct flag may have to be passed before the +sbt flag on the
command line (in case no CPU topology has been automatically
detected).
For more information, see erlang:system_flag(scheduler_bind_type,SchedulerBindType).
+sctCpuTopology
* <Id>=integer();when0=<<Id>=<65535
* <IdRange>=<Id>-<Id>
* <IdOrIdRange>=<Id>|<IdRange>
* <IdList>=<IdOrIdRange>,<IdOrIdRange>|<IdOrIdRange>
* <LogicalIds>=L<IdList>
* <ThreadIds>=T<IdList>|t<IdList>
* <CoreIds>=C<IdList>|c<IdList>
* <ProcessorIds>=P<IdList>|p<IdList>
* <NodeIds>=N<IdList>|n<IdList>
* <IdDefs>=<LogicalIds><ThreadIds><CoreIds><ProcessorIds><NodeIds>|<LogicalIds><ThreadIds><CoreIds><NodeIds><ProcessorIds>
* CpuTopology=<IdDefs>:<IdDefs>|<IdDefs>
Upper-case letters signify real identifiers and lower-case letters
signify fake identifiers only used for description of the topology.
Identifiers passed as real identifiers may be used by the runtime
system when trying to access specific hardware and if they are not
correct the behavior is undefined. Faked logical CPU identifiers
are not accepted since there is no point in defining the CPU
topology without real logical CPU identifiers. Thread, core,
processor, and node identifiers may be left out. If left out,
thread id defaults to t0, core id defaults to c0, processor id
defaults to p0, and node id will be left undefined. Either each
logical processor must belong to one and only one NUMA node, or no
logical processors must belong to any NUMA nodes.
Both increasing and decreasing <IdRange>s are allowed.
NUMA node identifiers are system wide. That is, each NUMA node on
the system have to have a unique identifier. Processor identifiers
are also system wide. Core identifiers are processor wide. Thread
identifiers are core wide.
The order of the identifier types imply the hierarchy of the CPU
topology. Valid orders are either
<LogicalIds><ThreadIds><CoreIds><ProcessorIds><NodeIds>, or
<LogicalIds><ThreadIds><CoreIds><NodeIds><ProcessorIds>. That is,
thread is part of a core which is part of a processor which is part
of a NUMA node, or thread is part of a core which is part of a NUMA
node which is part of a processor. A cpu topology can consist of
both processor external, and processor internal NUMA nodes as long
as each logical processor belongs to one and only one NUMA node. If
<ProcessorIds> is left out, its default position will be before
<NodeIds>. That is, the default is processor external NUMA nodes.
If a list of identifiers is used in an <IdDefs>:
* <LogicalIds> have to be a list of identifiers.
* At least one other identifier type apart from <LogicalIds> also
have to have a list of identifiers.
* All lists of identifiers have to produce the same amount of
identifiers.
A simple example. A single quad core processor may be described
this way:
% erl +sct L0-3c0-3
1> erlang:system_info(cpu_topology).
[{processor,[{core,{logical,0}},
{core,{logical,1}},
{core,{logical,2}},
{core,{logical,3}}]}]
A little more complicated example. Two quad core processors. Each
processor in its own NUMA node. The ordering of logical processors
is a little weird. This in order to give a better example of
identifier lists:
% erl +sct L0-1,3-2c0-3p0N0:L7,4,6-5c0-3p1N1
1> erlang:system_info(cpu_topology).
[{node,[{processor,[{core,{logical,0}},
{core,{logical,1}},
{core,{logical,3}},
{core,{logical,2}}]}]},
{node,[{processor,[{core,{logical,7}},
{core,{logical,4}},
{core,{logical,6}},
{core,{logical,5}}]}]}]
As long as real identifiers are correct it is okay to pass a CPU
topology that is not a correct description of the CPU topology.
When used with care this can actually be very useful. This in order
to trick the emulator to bind its schedulers as you want. For
example, if you want to run multiple Erlang runtime systems on the
same machine, you want to reduce the amount of schedulers used and
manipulate the CPU topology so that they bind to different logical
CPUs. An example, with two Erlang runtime systems on a quad core
machine:
% erl +sct L0-3c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname one
% erl +sct L3-0c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname two
In this example each runtime system have two schedulers each
online, and all schedulers online will run on different cores. If
we change to one scheduler online on one runtime system, and three
schedulers online on the other, all schedulers online will still
run on different cores.
Note that a faked CPU topology that does not reflect how the real
CPU topology looks like is likely to decrease the performance of
the runtime system.
For more information, see erlang:system_flag(cpu_topology,CpuTopology).
+ssssize
Suggested stack size, in kilowords, for scheduler threads. Valid
range is 4-8192 kilowords. The default stack size is OS
dependent.
+TLevel
Enables modified timing and sets the modified timing level.
Currently valid range is 0-9. The timing of the runtime system
will change. A high level usually means a greater change than a
low level. Changing the timing can be very useful for finding
timing related bugs.
Currently, modified timing affects the following:
Processspawning
A process calling spawn, spawn_link, spawn_monitor, or
spawn_opt will be scheduled out immediately after completing
the call. When higher modified timing levels are used, the
caller will also sleep for a while after being scheduled out.
Contextreductions
The amount of reductions a process is a allowed to
use before being scheduled out is increased or
reduced.
Inputreductions
The amount of reductions performed before checking I/O
is increased or reduced.
NOTE: Performance will suffer when modified timing is enabled. This
flag is only intended for testing and debugging. Also note that
return_to and return_from trace messages will be lost when tracing on
the spawn BIFs. This flag may be removed or changed at any time
without prior notice.
+V Makes the emulator print out its version number.
+v Verbose.
+Ww|i
Sets the mapping of warning messages for error_logger. Messages
sent to the error logger using one of the warning routines can be
mapped either to errors (default), warnings ( +Ww), or info
reports ( +Wi). The current mapping can be retrieved using
error_logger:warning_map/0. See error_logger(3erl) for further
information.

ENVIRONMENTVARIABLES

ERL_CRASH_DUMP
If the emulator needs to write a crash dump, the value of this
variable will be the file name of the crash dump file. If the
variable is not set, the name of the crash dump file will be
erl_crash.dump in the current directory.
ERL_CRASH_DUMP_NICEUnixsystems: If the emulator needs to write a crash dump, it
will use the value of this variable to set the nice value for the
process, thus lowering its priority. The allowable range is 1
through 39 (higher values will be replaced with 39). The highest
value, 39, will give the process the lowest priority.
ERL_CRASH_DUMP_SECONDSUnixsystems: This variable gives the number of seconds that the
emulator will be allowed to spend writing a crash dump. When the
given number of seconds have elapsed, the emulator will be
terminated by a SIGALRM signal.
ERL_AFLAGS
The content of this environment variable will be added to the
beginning of the command line for erl.
The -extra flag is treated specially. Its scope ends at the end
of the environment variable content. Arguments following an
-extra flag are moved on the command line into the -extra
section, i.e. the end of the command line following after an
-extra flag.
ERL_ZFLAGSand ERL_FLAGS
The content of these environment variables will be added to the
end of the command line for erl.
The -extra flag is treated specially. Its scope ends at the end
of the environment variable content. Arguments following an
-extra flag are moved on the command line into the -extra
section, i.e. the end of the command line following after an
-extra flag.
ERL_LIBS
This environment variable contains a list of additional library
directories that the code server will search for applications and
add to the code path. See code(3erl).
ERL_EPMD_PORT
This environment variable can contain the port number to use when
communicating with epmd. The default port will work fine in most
cases. A different port can be specified to allow nodes of
independent clusters to co-exist on the same host. All nodes in a
cluster must use the same epmd port number.